A "left shift" is a phrase used to note that there are a high number of young, immature white blood cells present. Most commonly, this means that there is an infection or inflammation present and the bone marrow is producing more WBCs and releasing them into the blood before they are fully mature. - A larger left shift indicates a larger neutrophil consumption in the blood. - A larger left shift represents a more severe bacterial infection. - Left shift reflects the severity of a bacterial infection consuming neutrophils